1. Field of the Invention
The present invention relates to a liquid jetting apparatus which jets a liquid from nozzles.
2. Description of the Related Art
As a liquid jetting apparatus which jets a liquid from nozzles, Japanese Patent Application laid-open No. 2006-21423 describes an image forming apparatus which jets an ink from the nozzles to perform printing. In the image forming apparatus described in Japanese Patent Application laid-open No. 2006-21423, a belt is wound and applied between two pulleys which are aligned in a scanning direction with a spacing distance therebetween, and a carriage which carries an ink jethead is connected to a portion of the belt positioned between the two pulleys. In this structure, in a case that the belt is driven to travel by rotating the pulleys, the carriage is moved in the scanning direction. In this situation, the carriage is guided along a sliding surface provided in a plate (support plate). One of the two pulleys is provided in the plate, and the other pulley is held by a pulley holder (holder) which is movable with respect to the plate in the scanning direction. The pulley holder is biased or urged by a spring toward a direction in which the other pulley is pressed to the belt. Accordingly, tension depending on biasing force of the spring is applied to the belt.
In the image forming apparatus described in Japanese Patent Application laid-open No. 2006-21423, the tension of the belt is temporarily changed at the time of moving the carriage. In this situation, since the pulley holder is not fixed to the plate, the pulley holder is moved in the scanning direction (so-called autotension) so that the tension of the belt and the biasing force of the spring are balanced in the scanning direction. Thus, in a case that tension originally applied to the belt is small, there is fear that a moving amount of the holder is large to make the belt loose, which causes difficulty in the travel of the belt.
In a case that the biasing force of the spring is made to be larger to make the tension applied to the belt larger, the situation, in which the belt is loosen to have difficulty in traveling, is not occurred. In this case, however, burden on a motor rotating the pulleys to move the carriage is increased. Therefore, it is required to use a large motor, which increases the size of the apparatus.
In view of the above, the inventor of the present teaching has considered to adopt a type (so-called fixed tension) in which the pulley holder is fixed to the plate by a bolt and the like at a position at which force received from the spring and force received from the belt are balanced in the scanning direction, in the image forming apparatus described in Japanese Patent Application laid-open No. 2006-21423. In this case, even when the tension of the belt is changed by moving the carriage, the pulley holder is not moved. Thus, even when the tension of the belt is small, the travel of the belt is less likely to be affected.
In this case, however, in a case that the position of the pulley holder is deviated in a direction, which is parallel to a plane perpendicular to a stacking direction of the pulley holder and the plate, at the time of fixing the pulley holder to the plate, even though the deviation is not so large (for example, about 0.5 mm), the tension applied to the belt is changed significantly.
An object of the present teaching is to provide a liquid jetting apparatus which is capable of applying a predetermined tension to a belt reliably in a case that a so-called fixed tension is adopted in order to apply the predetermined tension to the belt which is wound and applied between pulleys to move a carriage.